FIG. 1 illustrates a state-of-the-art Hewlett-Packard inkjet print cartridge 10 which the present invention was designed to improve.
Print cartridge 10 includes an ink reservoir 12 and a printhead 14, where the printhead 14 is formed using Tape Automated Bonding (TAB). The printhead 14 includes a nozzle member 16 comprising two parallel columns of offset nozzles 17 formed in a flexible polymer tape 18 by, for example, laser ablation. The tape 18 may be purchased commercially as Kapton.TM. tape, available from 3M Corporation. Other suitable tape may be Upilex.TM. or its equivalent.
A back surface of tape 18, shown in FIG. 2, includes conductive traces 19 formed thereon using a conventional photolithographic etching and/or plating process. These conductive traces 19 are terminated by large contact pads 20 designed to interconnect with printer electrodes, providing externally generated energization signals to the printhead.
The ends of traces 19 are bonded to exposed electrodes 29 (FIG. 3) on a rectangular silicon substrate 28 mounted to the back of nozzle member 16. FIG. 3 is a cross-sectional view along line 3--3 in FIG. 2 showing the connection of traces 19 to electrodes 29 on substrate 28. A barrier layer 30 (formed of, for example, photoresist) is patterned to define ink ejection chambers (not shown) into which ink flows via ink channels 32. Ink is ejected from nozzles 17 as droplets 36 when the ink ejection elements (e.g., heater resistors) are energized by signals applied to electrodes 29. An insulator 42 is formed on substrate 28 to insulate traces 19 from substrate 28.
Windows 44 and 45 extend through tape 18 and are used to facilitate bonding of the ends of the conductive traces 19 to electrodes 29 on substrate 28. Windows 44 and 45 may be formed using conventional photolithographic techniques.
FIG. 4 is a front view of tape 18 removed from print cartridge 10 and prior to windows 44 and 45 being filled with an encapsulant.
After bonding traces 19 to electrodes 29, traces 19 and electrodes 29 remain exposed through the rectangular windows 45 and 46 and must now be protected from ink and physical damage. To provide such protection, beads of an adhesive 48, shown in FIGS. 1 and 3, are dispensed over the exposed traces 19 to encapsulate the traces 19. Adhesive 48 may be a UV cureable adhesive or any other suitable adhesive.
In the manufacturing of the print cartridge 10 shown in FIG. 1, it has been found difficult to dispense the proper amount of adhesive 48 to fully encapsulate traces 19 while at the same time preventing adhesive 48 from flowing too near or over one of the nozzles 17. Adhesive 48 generally has a low viscosity. This low viscosity causes the adhesive 48 which overflows out of the top of windows 44 and 45 to flow easily towards nozzles 17. This adhesive 48, once cured, causes problems with different aspects of the print cartridge 10, including wiping of the nozzles 17 and capping of the nozzle member 16.
FIG. 5 is a top-down view of the nozzle and window portion of printhead 14 showing adhesive 48 overflowing out of windows 44 and 45 and flowing over one or more end nozzles 17. FIG. 6 is a magnified cross-sectional view along line 6--6 in FIG. 5 showing the overflow of adhesive 48 out of window 45 and over nozzle 17.
The main technique used by Hewlett-Packard in the past to prevent the adhesive 48 from flowing too near the nozzles 17 was to adjust the fluid pressure in the adhesive dispenser to change the amount of adhesive 48 being dispensed to match the variable amount needed to fill the window 44 or 45. It was discovered that this was not a satisfactory solution because the variation in the window 44/45 size is relatively great from print cartridge to print cartridge as well as over time. Therefore, the fluid pressure would have to be adjusted for each print cartridge 10 manufactured. This adjustment process also resulted in reduced manufacturing yield since the process eventually produces faulty print cartridges before any problem with adhesive overflow is caught.
What is needed is an inexpensive and reliable method to inhibit the flow of adhesive 48 in a controllable manner over the polymer tape 18 surface.